The present invention relates to a catalyst composition for the production of polyamide/copolyamide which comprises an alkali metal hypophosphite and an organic or inorganic salt, which is not an alkali metal hypophosphite. More particularly, the present invention relates to a catalyst composition comprising an alkali metal hypophosphite as the primary catalyst and an organic or inorganic salt, which is not an alkali metal hypophosphite, as a cocatalyst, to increase the reaction rate during the polymerization of polyamide and/or copolyamide.
Polyamide and copolyamide have been widely used as fibers and engineering plastics. In its application as engineering plastics, polyamide and copolyamide are mainly used to make automobile parts, electric and electronic components, electric wire coatings, tool boxes, and coasters. As fibers, polyamide and copolyamide are used in making fishing nets, carpets, tires and brushes (including toothbrushes, cosmetic brushes and grinding brushes) as well as stockings.
Polyamide.copolyamide can be synthesized using the conventional continuous reaction process, or the reactive extrusion process, which was developed only recently. In reactive extrusion process to synthesize polymers, the extruder is used as a mini-reactor. First, monomers, co-monomers and/or prepolymers are fed into the extruder. The reactants react inside the extruder to produce the polymer material, which is then extruded from the extruder to provide the final product.
The reactive extrusion technology has the following advantages: First, it provides a high area-to-volume ratio for excellent heat transfer. Second, it provides excellent mixing action during the polymerization reaction. This is particularly advantageous for highly viscous fluids, which can also be transported through the reactor. Third, it can be adapted to provide multiple temperature zones, each having a distinct temperature. Fourth, the reactive extruder can be adapted to provide multiple exhaust or vacuum sections, each vacuum section can have the same or different of vacuum. Fifth, it involves a continuous reaction-extrusion process. Sixth, the resident time involved in the process is very short; therefore, the productivity can be very high per unit time. Seventh, the reactive extrusion process requires a much simpler apparatus than most other conventional commercial reactors. Finally, with the reactive extrusion process, the composition of the feed monomers can be conveniently varied; this greatly enhances the utilization efficiency of the capital investment, and is particularly advantageous for production lines that make relatively small quantities of a large variety of products.
With the above mentioned advantages, the reactive extrusion technology potentially can become one of the best methods to produce polymers and copolymers. However, when the reactive extrusion technology is applied to the production of polyamide or copolyamide, current catalyst systems do not provide fast enough reaction rate to take full advantage of this evolving technology. The reaction must be very fast so that the polymerization reaction to make polyamide or copolyamide can be completed in the extruder before they are extruded.